Sexton grew up in Rockwell City on the family farm and graduated from Rockwell City High School. He earned an AAS Degree in Ag Business from Iowa Lakes Community College. Mike and his wife, Becky, started two small businesses which they currently manage. Twin Lakes Environmental Services is a consulting firm with a goal of keeping family farmers on their land. Real Time Ag is a software company specializing in keeping producers current with regulatory reporting. The two companies go hand-in-hand. They employ seven employees. Mike continues to operate the family farm in Calhoun County.

Sexton was first elected to the State Senate in 1998. He chose not to run for reelection in 2002 so he could spend more time with his children while they were still at home.

Sexton and his wife have five children and attend Rockwell City Presbyterian Church.